Exploring, drilling and completing hydrocarbon wells are generally complicated, time consuming and ultimately very expensive endeavors. As a result, over the years increased attention has been paid to monitoring and maintaining the health of such wells. Significant premiums are placed on maximizing the total hydrocarbon recovery, recovery rate, and extending the overall life of the well as much as possible. Thus, logging applications for monitoring of well conditions play a significant role in the life of the well. Similarly, significant importance is placed on well intervention applications, such as clean-out techniques which may be utilized to remove debris from the well so as to ensure unobstructed hydrocarbon recovery.
Clean out techniques as indicated above may be employed for the removal of loose debris from within the well. However, in many cases, debris may be present within the well that is of a more challenging nature. For example, debris often accumulates within a well in the form of ‘scale’. As opposed to loose debris, scale is the build-up or caking of deposits at the surface of the well wall. For example, the well wall may be a smooth steel casing within the well that is configured for the rapid uphole transfer of hydrocarbons and other fluids from a formation. However, a build-up of irregular occlusive scale may occur at the inner surface of the casing restricting flow there through. Indeed, scale may even form over perforations in the casing, thereby also hampering hydrocarbon flow into the well from the surrounding formation.
Unfortunately, scale build-up within a well may take place in a fairly rapid manner. For example, it would not be uncommon for hydrocarbon production to decrease on the order of several thousand barrels per day once a significant amount of scale begins to accumulate at the well wall. Furthermore, while a variety of conventional techniques are available for addressing scale, hundreds of millions of dollars are nevertheless lost every year to the curing of scale problems. That is, as described below, current scale removal techniques remain fairly inefficient, leaving significant production time lost to the application of the techniques.
Scale build-up generally results from the presence of water within the well. This may be the result of water production by the well or the intentional introduction of water to the well, for example, by a water injector to enhance hydrocarbon recovery. Regardless, the presence of water may ultimately lead to mineral deposits such as calcium carbonate, barium sulfate, and others which may be prone to crystallize and build-up in the form of scale at the inner wall of the well as noted above. Due to the nature of the scale, chemical techniques such as the introduction of hydrochloric or other acids are often employed to break up the scale. Unfortunately, however, the introduction of acids is generally followed by a soak period which increases the amount of production time lost. Furthermore, acids may not be particularly effective at breaking up harder scale deposits and may even leave the well wall primed for future scale build-up. Therefore, mechanical techniques as described below are often employed for scale removal.
Scale may be removed by a variety of mechanical techniques such as the use of explosives, impact bits, and milling. However, these techniques include the drawback of potentially damaging the well itself. Furthermore, the use of impact bits and milling generally fails to remove scale in its entirety. Rather, a small layer of scale is generally left behind which may act as a seed layer in encouraging new scale growth. As a result of these drawbacks, fluid mechanical jetting tools as described below may be most often employed for scale removal.
Water jetting tools are often deployed within a well to remove scale build-up as described above. A water jet tool may be dropped into the well via coiled tubing and include a rotating head for jetting water toward the well wall in order to fracture and dislodge the scale. The rotating head may include water dispensing arms that project outward from a central axis of the tool and toward the well wall. Additionally, in many cases, the water may include an abrasive in order to aid in the cutting into and fracturing of the scale as indicated.
For effective removal of scale with a water jetting tool as noted above, the water dispensing arms are securely pre-positioned with an outer diameter that is as close as possible to the scale. In this manner, the full force of the water may be substantially taken advantage of. Unfortunately, however, the thickness of the scale within the well may be quite variable. For example, there may be regions of the well with minimal scale buildup, whereas a maximum scale thickness of over an inch may be present in other regions of the well. In such a scenario, the arms of the water jet tool may be securely positioned at an outer diameter that is within about half of an inch of the maximum scale thickness. Thus, a water jet application of the tool through the well may remove a substantial amount of scale in well regions of maximum scale thickness. However, in other well regions of lesser scale thickness, scale buildup may remain largely unaffected.
The variability in scale thickness may largely determine the effectiveness of a given run through of the tool in the well. For example, the arms of the tool may be set with a drift ring retainer of a given outer diameter and the tool run through the well as part of the scale removal application. However, only a portion of the scale may be removed down to a certain level in regions of maximum scale thickness. Thus, the tool may then be removed from the well and the arms securely repositioned at a larger outer diameter with a larger drift ring retainer by an operator at the oilfield.
A subsequent run of the tool through the well may then take place. This process may continue several times until the scale is fully removed. Indeed, today there are about 30 different standard drift ring sizes that are commercially available so as to allow for a significant number of runs of the tool through the well with differently sized or positioned tool arms. Unfortunately, each of these separate runs through the well may take between about 5 and 12 hours or more, depending on the depth of the well. Thus, with the trend toward wells of greater depths, the time lost in order to resize the tool arms for continuing the scale removal is increasing. As such, the expense of the overall hydrocarbon recovery effort is substantially increasing as well.